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  You can use sed to add a string after a particular substring
 in a text.
 To add creating a new line under the substring:
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 sed  '/\<substring>\/a <text to insert>/' <file>
 Where:
 1 - The '\' is an escape character,
 2 - '/a' indicates 'after match'.
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 If you wanted you insert before the match, use '/i'.
 If you want to insert in the same line as the substring, do
 this:
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 sed 's/<substring>/ <text to insert>/' <file>
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